modetest: add page (tldr-pages#17656)

Author: Managor

pages/linux/modetest.md

@@ -0,0 +1,12 @@
+# modetest
+
+> Diagnose Direct Rendering Manager and Kernel Mode Setting.
+> More information: <https://xilinx-wiki.atlassian.net/wiki/spaces/A/pages/18841850/Video_Mixer#modetest>.
+
+- List connectors and their available modes for a specific driver:
+
+`modetest -M {{mgag200}} -c`
+
+- Set the resolution of a connector:
+
+`sudo modetest -M {{mgag200}} -s {{connector_id}}:{{1600}}x{{1200}}`